The present disclosure relates generally to integrated motor drive systems and more particularly to integrated regenerative AC drives with solid-state precharging circuitry. Integrated AC motor drives provide a single package product for powering AC electrical motors using converted power from an AC input source. Regenerative drives are operable in a motoring mode in which power is converted from the AC input source for driving a motor load, as well as a regenerating mode in which power from the motor drive is provided to the AC source. Voltage source converter type AC drives include a DC circuit with one or more capacitors providing a DC bus voltage from which an output inverter derives power for driving a motor load. During startup, the initial charging of the DC bus capacitance can result in excessive inrush current which can damage or degrade motor drive components and associated protective equipment.
Conventional integrated regenerative AC motor drives have accordingly provided an AC contactor or relays situated between the AC power source terminals and an input rectifier, where one or more AC input lines include contact terminals connected in parallel with a current limiting device to limit inrush current during power application. At power up, the relay or contactor is maintained in an “off” state with the contacts “open” such that the incoming AC currents flow through the current limiting devices to thereby limit the inrush current. Once the DC link capacitance has been properly precharged, the contactor or relay is activated to close the contacts, thereby bypassing the current limiting devices for normal operation.
Contactors and relays, however, are costly and occupy valuable space in an integrated motor drive. Moreover, power for energizing a relay or contactor coil must be derived from the input power, and this control power must be available even if multiphase AC input power wiring errors occur and/or phase loss problems arise. In addition, contactors and relays are subject to wear and degradation, and I/O and wiring requirements must be accommodated in the limited space of modern integrated motor drives. Thus, there remains a need for improved inrush current limiting designs allowing controlled charging of DC bus capacitors for integrated regenerative motor drives.